Apparatus for vitrifcation of hazardous waste

ABSTRACT

Apparatus (10) and a method for vitrifying hazardous waste includes a melting vessel (12) in which hazardous waste and any other necessary components for forming a glassy mixture upon heating are introduced for heating by a heater (38), and a metallic containment vessel (46) of the apparatus receives the melting vessel so as to receive and contain any material that exits the melting vessel upon failure. Any failure of the melting vessel (12) is detected by a sensor (48). Different embodiments of the heater (38) provide current flow through molten material (18) being heated, induction heating and electric resistance heating. A stirrer (39) can be utilized to mix the material (18) during the heating. The containment vessel (46) is preferably hermetically sealed around the melting vessel (12) to contain gases as well as any melted material received from the failed melting vessel (12). The sensing of the failure can be either by a pressure change in the hermetically sealed chamber (58) or by sensing of the presence of material received by the containment vessel (46) from the failed melting vessel (12) such as by electrical circuit type detection.

TECHNICAL FIELD

This invention relates to apparatus and a method for vitrifyinghazardous waste.

BACKGROUND ART

Vitrification of waste materials has previously been accomplished inceramic lined melting vessels that are capable of being heated torelatively high temperatures such as on the order of about 1500° C. to1600° C. Such heating as disclosed by U.S. Pat. No. 4,820,328 Roberts etal can be utilized to vitrify waste asbestos by a high temperaturemelting process. Furthermore, as disclosed by U.S. Pat. No. 5,100,453Richards such high temperature melting can be utilized to recycle glassfibers such as of the type utilized for building insulation. Likewise,incinerator fly ash can also be vitrified by such high temperaturemelting in a ceramic melting vessel. During such processing, the wasteand any other necessary components to form a glassy material uponheating are introduced into the ceramic melting vessel, and the meltedmaterial permeates into seams or any cracks in the ceramic meltingvessel sufficiently to cool and thereby seal the vessel so that there isno leakage.

Vitrification of hazardous waste at a lower temperature such as on theorder of about 1000° to 1100° C. has also previously been done byheating thereof within a metallic melting vessel. When hazardous wastesuch as nuclear waste or heavy metals etc. is vitrified, the resultantmelted mixture can be delivered into a container for storage uponcooling. However, the metallic melting vessel can fail during use and,in such case, hazardous waste in the melting vessel can contaminate thefacility in which the processing is being performed. Such contaminationcan be a particular problem when nuclear waste processing is involved.Furthermore, heating in a metallic melting vessel has previously beendone by passing an electrical current through the melted materialbetween the metallic melting vessel and a stirrer that mixes thematerial being heated. Thus, the metallic melting vessel and the stirreract as the electrodes between which the current flows for the heating asmixing takes place. This type of heating is believed to provide superiorresults due to the direct generation of heat within the melted materialby the passage of electric current uniformly through the melt betweenthe stirrer and the melting vessel.

DISCLOSURE OF INVENTION

Objects of the present invention are to provide improved apparatus and amethod for vitrifying hazardous waste in a manner that providescontainment of the waste in case of failure of the melting vessel inwhich the hazardous waste is heated for the vitrification.

In carrying out the above objects, apparatus for vitrifying hazardouswaste in accordance with the present invention includes a metallicmelting vessel for receiving hazardous waste and any other necessarycomponents for forming a glassy material upon heating. A heater of theapparatus provides heating of material in the melting vessel. Theapparatus also includes a metallic containment vessel in which themelting vessel is located so the containment vessel upon failure of themelting vessel receives and contains any material that exits the failedmelting vessel. A sensor of the apparatus is also provided for detectingthe failure of the melting vessel.

Different embodiments of the heater are disclosed. One type of heaterdisclosed passes electrical current through molten material within themelting vessel to provide the heating, with one such heater embodimenthaving an electrical voltage across the melting vessel and an electrodewithin the molten material in the melting vessel to pass the electricalcurrent through the molten material to provide heating thereof, and withanother such embodiment having an electrical voltage across a pair ofelectrodes in the molten material in the melting vessel to pass anelectrical current through the molten material to provide heatingthereof. Another embodiment of the heater includes induction coils forheating the material within the melting vessel by induction heating ofthe melting vessel. A further embodiment of the heater includeselectrical resistance elements for heating the material within themelting vessel by electric resistance heating of the melting vessel.

The apparatus for vitrifying hazardous waste is also disclosed asincluding a stirrer for mixing the material being heated.

In the preferred construction of the apparatus, the containment vesselis hermetically sealed around the melting vessel to form an enclosedchamber that contains gases as well as any other material that exits thefailed melting vessel.

Different embodiments of the sensor are disclosed. In one embodiment,the sensor is communicated with the hermetically sealed chamber betweenthe melting vessel and the containment vessel to detect a change inpressure within the hermetically sealed chamber when the melting vesselfails to thereby detect such failure. In other embodiments, the sensorfor detecting failure of the melting vessel senses the presence ofmaterial received by the containment vessel from the failed meltingvessel and preferably includes an electrical circuit that detects thepresence of material received by the containment vessel from the failedmelting vessel. In one embodiment, the electrical circuit of the sensorincludes a pair of electrical probes that are located between themelting and containment vessels and are normally electrically isolatedfrom each other until material received by the containment vessel fromthe failed melting vessel electrically connects the probes to eachother. In another embodiment, the electrical circuit includes a flowpath that is located between the melting and containment vessels andthat is normally closed but is opened by the presence of materialreceived by the containment vessel from the failed melting vessel.

In the preferred construction, the apparatus also includes anothersensor for sensing failure of the melting vessel so as to provide afail-safe detection of the melting vessel failure. Thus, there is a pairof sensors for detecting the failure of the melting vessel, and eachsensor is preferably either a sensor that is communicated with thehermetically sealed chamber between the melting vessel and thecontainment vessel to sense a change in pressure when the melting vesselfails, or a sensor including an electrical circuit that senses thepresence of material received within the containment vessel from thefailed melting vessel.

In carrying out the objects of the invention, the method for vitrifyinghazardous waste is performed by introducing hazardous waste and anyother necessary components for forming a glassy material upon heatinginto a metallic melting vessel. Heating of the material within themelting vessel is performed in any suitable manner. The melting vesselis also located within a metallic containment vessel so as to containany material that exits the melting vessel upon failure of the meltingvessel. Sensing for a failure of the melting vessel is also performed toprovide an indication that the processing should be terminated so thatthe hazardous waste does not contaminate the facility in which theprocessing is being performed.

The method for vitrifying hazardous waste can be performed with theheating conducted in different ways including: (a) passing electricalcurrent through molten material within the melting vessel; (b) usinginduction heating; and (c) using electric resistance heating.

In performing the method for vitrifying hazardous waste, the materialcan also be stirred during the heating.

In one preferred practice of the method, the sensing for failure of themelting vessel is performed by detecting a change in pressure of thehermetically sealed chamber between the melting and the containmentvessels.

In another preferred practice of the method, the sensing for failure ofthe melting vessel is performed by detecting the presence of materialreceived within the containment vessel from the failed melting vessel.The presence of material received within the containment vessel from thefailed melting vessel is disclosed as being detected by an electricalcircuit.

The most preferred practice of the method utilizes a pair of sensors todetect failure of the melting vessel so that this detection is performedin a fail-safe manner.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an elevational view taken in section through apparatusconstructed in accordance with the present invention to provide themethod thereof for vitrifying hazardous waste;

FIG. 2 is a partial view similar to FIG. 1 but with another type ofheater which like the FIG. 1 embodiment also passes electrical currentthrough molten material within the melting vessel to provide theheating;

FIG. 3 is a view similar to FIG. 2 but of another embodiment whichincludes an induction heater;

FIG. 4 is also a view similar to FIG. 2 but of a further embodimentwhich includes an electric resistance heater;

FIG. 5 is a view similar to each of FIGS. 1-4 and illustrates a stirrerwhich can be utilize to provide mixing of the material being heatedregardless of which type of heater is utilized;

FIG. 6 is a view that illustrates a pressure sensor for detectingfailure of a melting vessel of the apparatus;

FIG. 7 is a view that illustrates a normally open electrical circuitsensor for sensing the failure of the melting vessel; and

FIG. 8 is a view that illustrates a normally closed electrical circuitsensor for sensing the failure of the melting vessel.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, apparatus 10 constructed in accordance withthe present invention performs the method thereof for vitrifyinghazardous waste such as nuclear waste, heavy metals etc. This apparatusincludes a metallic melting vessel 12 having an inlet 14 for receivinghazardous waste and any other necessary components for forming a glassymaterial upon heating as is hereinafter more fully described. Themelting vessel 12 also has a gas outlet 16 through which gases generatedby the processing can flow outwardly for any necessary treatment priorto being released to the atmosphere. Molten material 18 within thevessel 12 is delivered through an outlet 20 with a lower entry end 22and an upper outer exit end 24 with a construction that functions like ateapot spout. Outlet 20 which has a tubular construction outwardly ofthe melting vessel 12 extends through a suitable heating insulation 26secured by an outer shell 28, and the outlet 20 is also surrounded by aheater 30 to maintain the material molten until it is delivered to asuitable container for cooling and consequent solidification. Likewise,a lower drain 32 of a metallic tubular construction extends through theinsulation 26 and is surrounded by an associated heater 34 with itsouter end closed by a water cooled plug 36 that can be removed to permitdrainage of the melting vessel 12 when necessary.

Heating of the material within the melting vessel 12 of apparatus 10 isaccomplished by a heater 38a providing electric current flow through thematerials in the molten state contained within the melting vessel. Inthe embodiment disclosed, current flow through the molten material isestablished between an electrode 40 and the vessel 12 by the applicationof electrical potentials 42 and 44. In order to commence current flow,it is necessary to introduce a preliminary amount of solid materialthrough the feed port 14 to contact the electrode 40. Auxiliaryelectrical resistance heaters 45 within the insulation 26 providesufficient heat to the solid material to bring it to a molten statecapable of conducting electric current between the electrode and themelting vessel. Following the start of electric melting via current flowbetween the electrode and the melting vessel, additional solid materialis fed to the melting vessel for continuous processing. Also, analternating current functions best in that it prevents plating ofcomponents on the electrode 40 or the melting vessel 12.

A metallic containment vessel 46 of the apparatus 10 shown in FIG. 1 islocated around the melting vessel 12 so the containment vessel uponfailure of the melting vessel receives and contains any material thatexits the failed melting vessel. Thus, any hazardous waste component ofmaterial that exits the failed melting vessel 12 will not contaminatethe facility in which the apparatus 10 is located but, rather will becontained within the containment vessel 46 which can then be properlyprocessed during a cleanup operation. Furthermore, apparatus 10 alsoincludes at least one sensor 48 for detecting failure of the meltingvessel as is hereinafter more fully described.

With continuing reference to FIG. 1, it will be noted that both themetallic melting vessel 12 and metallic containment vessel 46 arerespectively made from metal plates 50 and 51 that are secured by welds52 with these two vessels essentially being unitized with each otherafter completion of the assembly. Lower supports 54 provide thenecessary support between the floor plates 50 and 51 while a support rod55 extends downwardly from the containment vessel floor plate 51 throughthe insulation 26 to provide support for the unitized melting andcontainment vessels 12 and 46. Suitable unshown supports between thesidewall plates 50 and 51 of the melting and containment vessel 12 and46 are also provided and like all of the plates and supports are securedby associated welds.

The metal plates 50 and 51 are made from high temperature resistantmetal alloys such as alloys of nickel and chromium. Specific alloys thatcan be used are sold by Inco Alloys International, Inc. of Huntington,W. Va., United States of America under the trademark INCONEL. One suchalloy is designated INCONEL 601 and has a composition in parts by weightof: aluminum--1 part, chromium--23 parts, iron--14 parts, and nickel--61parts. Another such alloy is designated INCONEL 690 and has acomposition in parts by weight of: chromium--29 parts, iron--9 parts,and nickel--62 parts.

With reference to FIG. 2, another embodiment of the apparatus has thesame construction as the previously described embodiment and its heater38b like the previously described embodiment passes an electricalcurrent through molten material 18 within the melting vessel 12.However, this embodiment of the heater 38b includes a pair of electrodes40 and 41 located within the molten material 18 and having a voltageapplied across the electrodes by potentials 42 and 44 so as to providethe electrical current flow. Otherwise the embodiment of FIG. 2functions the same as the embodiment of FIG. 1.

With reference to FIG. 3, another embodiment of the apparatus 10 has thesame construction as the previously described embodiments except thatits heater 38c is of the induction heating type including inductioncoils 56 that provide induction heating of the melting vessel 12 and thematerial 18 within the melting vessel 12.

With reference to FIG. 4, a further embodiment of the apparatus has thesame construction as the previously described embodiment except that itsheater 38d is of the electric resistance heating type including electricresistance heaters 57 that provide the heating of the melting vessel 12and the material 18 within the melting vessel 12.

As illustrated in FIG. 5, the apparatus 10, which is shown as having aheater 38 that may be of any of the previously described types, can alsobe provided with a stirrer 39 for mixing the material 18 being heatedsuch as by rotation as shown by arrow 39'. It is also possible for thestirrer 39 to be an electrode and for the metallic melting vessel 12 tobe another electrode across which an electrical potential is applied sothat electrical current flow through the molten material 18 provides theheating as mixing takes place.

With reference to FIG. 1, the containment vessel 46 is preferablyhermetically sealed around the melting vessel 12 to form an enclosedchamber 58. Such an enclosed chamber is preferable to having an openspace between the two vessels since any gas that exits the failedmelting vessel 12 will then also be contained within the containmentvessel 46 which would not be the case if the vessels are nothermetically sealed.

With additional reference to FIG. 6, one embodiment of the sensor 48a isillustrated as having a conduit 60 communicated with the hermeticallysealed chamber 58 between the melting vessel 12 and the containmentvessel 46 to detect a change in pressure within the hermetically sealedchamber when the melting vessel fails to thereby detect such failure.More specifically, the sensor 48a has a pressure gauge 62 which candetect the pressure change when there is a failure such as illustratedat 64 between the floor and side wall plates 50 of the melting vessel12. Such pressure change may be an increase in pressure if a vacuum isinitially drawn in the chamber 58 or may also be a decrease in pressureif the chamber is initially pressurized.

With reference to FIGS. 7 and 8, two further embodiments 48b and 48c ofthe sensor are constructed to detect failure of the melting vessel 12 bysensing the presence of material 18 received by the containment vessel46 from the failed melting vessel 12. Each of the sensors 48b and 48cincludes an electric circuit 66 that detects the presence of materialreceived by the containment vessel 46 from the failed melting vessel 12.

In the embodiment of the sensor 48b shown in FIG. 7, the electricalcircuit 66 includes a pair of electrical probes 68 that are locatedbetween the melting and containment vessels 12 and 46 and are normallyelectrically isolated from each other with their lower ends suspendedjust above the containment vessel floor plate 51 in a spacedrelationship thereto and with respect to each other. Material 18received from the melting vessel 12 upon failure thereof such as throughthe failure 64 indicated electrically connects the lower ends of theprobe 68 to complete the electrical circuit 66 and thereby provide anindication of the failure.

With reference to FIG. 8, the embodiment of the sensor 48c has theelectrical circuit 66 thereof located between the melting andcontainment vessels 12 and 46 and having a meltable fuse 70 extendingbetween the lower ends of the probes 68. When the material 18 isreceived from the failed melting vessel 12 such as through the failure64 shown, the fuse 70 is melted to open the circuit 66 as the probes 68then become electrically isolated from each other as compared to beingelectrically connected when the fuse is in place for the relative levelof electric potential between the electrical probes.

In the preferred construction of the apparatus 10 shown in FIG. 1, thereare at least two of the sensors for sensing the failure of the meltingvessel 12. These sensors are most preferably of the type illustrated inFIGS. 6, 7 and 8. More specifically, as illustrated, there are two ofthe sensors 48 having the electrical circuit 66 and are located atopposite sides of the unitized melting and containment vessels 12 and46. Suitable openings may be provided in the floor supports 54 so thatthe material received can flow back and forth so that failure at anypart of the melting vessel 12 will activate these material presencesensing type sensors. Furthermore, the apparatus 10 is illustrated ashaving the pressure sensor 48 at its upper left side as well as theother two sensors. Suitable openings can also be provided in the unshownsupports between the side wall plates 50 and 51 as well as in the floorsupports 54 so that the entire extent of the hermetically sealed chamber58 is communicated with the pressure sensor 48a for its operation whenthis type of sensor is used.

The hazardous waste vitrifying method of the invention is performed byintroducing the hazardous waste and any other necessary components forforming a glassy material upon heating through the inlet 14 into themetallic melting vessel 12. Heating of the material 18 within themelting vessel 12 is performed while locating the melting vessel withinthe metallic containment vessel 46 to contain any material that exitsthe melting vessel upon failure of the melting vessel. Sensing of thisfailure by at least one of the sensors 48 provides an indication thatthe processing should be terminated.

The heating performed during the method can be done in any suitable waysuch as by any of the types of heaters previously described. Morespecifically, the heating can be performed by passing electrical currentthrough the molten material 18 within the melting vessel 12, by usinginduction heating, or by using electric resistance heating, etc.

In performing the method for vitrifying hazardous waste, the material 18can be stirred as previously described in connection with FIG. 5 duringthe heating. Other conventional methods of mixing can also be utilizedsuch as bubbling.

As discussed above, the sensing for the failure of the melting vessel 12can be performed by detecting a change in the pressure of thehermetically sealed chamber 58 between the melting and containmentvessels 12 and 46 and can also be performed by detecting the presence ofmaterial received within the containment vessel from the failed meltingvessel, with this latter type of detection preferably being performed byan electrical circuit. Furthermore, as previously mentioned, the methodis most preferably performed by utilizing a pair of the sensors todetect failure of the melting vessel 12 in a fail-safe manner.

While the best modes for practicing the invention have been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. Apparatus for vitrifying hazardous waste,comprising:a metallic melting vessel for receiving hazardous waste andany other necessary components for forming a glassy material uponheating; a heater that passes an electrical current through moltenmaterial within the melting vessel to provide heating thereof; ametallic containment vessel in which the melting vessel is located sothe containment vessel upon failure of the melting vessel receives andcontains any material that exits the failed melting vessel; and a sensorthat is located externally of the melting vessel and that detectsfailure of the melting vessel.
 2. Apparatus for vitrifying hazardouswaste as in claim 1 further including a stirrer for mixing the materialbeing heated.
 3. Apparatus for vitrifying hazardous waste comprising:ametallic melting vessel for receiving hazardous waste and any othernecessary components for forming a glassy material upon heating; aheater for heating material within the melting vessel; a metalliccontainment vessel in which the melting vessel is located so thecontainment vessel upon failure of the melting vessel receives andcontains any material that exits the failed melting vessel, thecontainment vessel being hermetically sealed around the melting vesselto form an enclosed chamber; and a sensor that is located externally ofthe melting vessel and that is communicated with the hermetically sealedchamber between the melting vessel and the containment vessel to detecta change in pressure within the hermetically sealed chamber when themelting vessel fails to thereby detect such failure.
 4. Apparatus forvitrifying hazardous waste as in claim 1 wherein the sensor fordetecting failure of the melting vessel senses the presence of materialreceived by the containment vessel from the failed melting vessel. 5.Apparatus for vitrifying hazardous waste as in claim 4 wherein thesensor includes an electrical circuit that detects the presence ofmaterial received by the containment vessel from the failed meltingvessel.
 6. Apparatus for vitrifying hazardous waste as in claim 5wherein the electrical circuit of the sensor includes a pair ofelectrical probes that are located between the melting and containmentvessels and are normally electrically isolated from each other untilmaterial received by the containment vessel from the failed meltingvessel electrically connects the probes to each other.
 7. Apparatus forvitrifying hazardous waste as in claim 5 wherein the electrical circuitof the sensor includes a flow path that is located between the meltingand containment vessels and that is normally closed but is opened by thepresence of material received by the containment vessel from the failedmelting vessel.
 8. Apparatus as in claim 1 further including anothersensor that is located externally of the melting vessel and that detectsfailure of the melting vessel.
 9. Apparatus for vitrifying hazardouswaste material comprising:a metallic melting vessel for receivinghazardous waste and any other necessary components for forming a glassymaterial upon heating; a heater for heating material within the meltingvessel; a metallic containment vessel in which the melting vessel islocated so the containment vessel upon failure of the melting vesselreceives and contains any material that exits the failed melting vessel,the containment vessel being hermetically sealed around the meltingvessel to provide a hermetically sealed chamber therebetween; a sensorthat is located externally of the melting vessel and that detectsfailure of the melting vessel; and another sensor that is locatedexternally of the melting vessel and that is communicated with thehermetically sealed chamber between the melting vessel and thecontainment vessel to sense a change in pressure when the melting vesselfails.
 10. Apparatus as in claim 1 wherein the heater has an electrodereceived within molten material in the melting vessel and passes anelectrical current between the electrode and the melting vessel throughthe molten material to heat the molten material.
 11. Apparatus as inclaim 1 wherein the heater includes a pair of electrodes within themolten material and between which an electrical current is passedthrough the molten material to heat the molten material.
 12. Apparatusas in claim 1 further including another heater that includes inductioncoils for heating the melting vessel and the material within the meltingvessel.
 13. Apparatus as in claim 1 further including another heaterthat includes electric resistance elements for heating the materialwithin the melting vessel.
 14. Apparatus for vitrifying hazardous wastematerial as in claim 1 further including another sensor that is locatedexternally of the melting vessel and has an electrical circuit thatsenses the presence of material received within the containment vesselfrom the failed melting vessel.